The following abbreviations are herewith defined, at least some of which are referred to within the following description.
3GPP Third Generation Partnership Project
ACK Positive-Acknowledgment
BLER Block Error Ratio
BPSK Binary Phase Shift Keying
C-RNTI Cell Radio Network Temporary Identifier
CAZAC Constant Amplitude Zero Auto Correction
CCA Clear Channel Assessment
CCE Control Channel Element
CDF Cumulative Distribution Function
CP Cyclic Prefix
CQI Channel Quality Information
CSI Channel State Information
CSS Common Search Space
CWS Contention Window Size
DCI Downlink Control Information
DL Downlink
DMTC Discover Signal Measurement Timing Configuration
DRX Discontinuous Reception
eCCA Enhanced Clear Channel Assessment
eNB Evolved Node B
EPDCCH Enhanced Physical Downlink Control Channel
ETSI European Telecommunications Standards Institute
FBE Frame Based Equipment
FDD Frequency Division Duplex
FDMA Frequency Division Multiple Access
FEC Forward Error Correction
HARQ Hybrid Automatic Repeat Request
LAA Licensed Assisted Access
LAA-RSSI Licensed Assisted Access Received Signal Strength Indicator
LBE Load Based Equipment
LBT Listen-Before-Talk
LTE Long Term Evolution
MAC Medium Access Control
MCL Minimum Coupling Loss
MCS Modulation and Coding Scheme
MU-MIMO Multi-User, Multiple-Input, Multiple-Output
NACK or NAK Negative-Acknowledgment
OFDM Orthogonal Frequency Division Multiplexing
PCell Primary Cell
PCID Physical Cell ID
PBCH Physical Broadcast Channel
PDCCH Physical Downlink Control Channel
PDSCH Physical Downlink Shared Channel
PHICH Physical Hybrid ARQ Indicator Channel
PLMN Public Land Mobile Network
PRACH Physical Random Access Channel
PRB Physical Resource Block
PUCCH Physical Uplink Control Channel
PUSCH Physical Uplink Shared Channel
RNTI Radio Network Temporary Identifier
QoS Quality of Service
QPSK Quadrature Phase Shift Keying
RAR Random Access Response
RRC Radio Resource Control
RRM Radio Resource Management
RSRP Reference Signal Received Power
RSRQ Reference Signal Received Quality
RSSI Received Signal Strength Indicator
RX Receive
SC-FDMA Single Carrier Frequency Division Multiple Access
SCell Secondary Cell
SCH Shared Channel
SFN System Frequency Number
SIB System Information Block
SNR Signal-to-Interference-Plus-Noise Ratio
SR Scheduling Request
TBS Transport Block Size
TDD Time-Division Duplex
TDM Time Division Multiplex
TX Transmit
UCI Uplink Control Information
UE User Entity/Equipment (Mobile Terminal)
UL Uplink
UMTS Universal Mobile Telecommunications System
VoIP Voice Over Internet Protocol
WiMAX Worldwide Interoperability for Microwave Access
In wireless communications networks, LAA facilitates an LTE system to use an unlicensed spectrum with assistance from a licensed carrier. LAA further aims to facilitate the fair coexistence with other technologies over the unlicensed spectrum and to satisfy various regulatory requirements in different countries and regions. In certain configurations, LAA operations may depend heavily on the LBT procedure. For example, if a channel is occupied, an eNB cannot transmit on that channel.
As may be appreciated, if a carrier has a significant amount of activity from other nodes (e.g., Wi-Fi, LAA, etc.) transmissions may be delayed. The delay of transmissions may apply to all transmissions including discovery signal transmissions, which are used for RRM measurements. The unpredictability of discovery signal transmissions may lead to various problems.
For example, RSRP measurements for LAA may be performed based on measurements of discovery signals. In one embodiment, a UE is provided a DMTC configuration, from which the UE derives time windows during which it expects to detect a discovery signal transmission. However, transmissions of discovery signals may be subject to the LBT procedure. Thus, if the channel is occupied, during the DMTC window, the discovery signal transmission is delayed or skipped. It should be noted that the DMTC window may be kept small to ensure that the UE power consumption for detecting and measuring the discovery signals remains manageable. If a discovery signal transmission is skipped or delayed, the UE physical layer may not provide a corresponding physical layer measurement to RRC.
A delay or skip in discovery signal transmissions by an eNB implies a delay in RSRP measurement samples by a UE. In various configurations, the UE may perform layer 3 filtering of physical layer RSRP measurements. The layer 3 filtering in LTE assumes that a measurement sample is made available at least once every 200 milliseconds (“ms”). If a discovery signal is considerably delayed, channel conditions may have changed significantly by the time the discovery signal is actually transmitted. However, a history in a layer 3 filter may cause the convergence of the filtered measurements to the new channel conditions to be slow.
Furthermore, RSRP measurements may not give a clear picture of activity on a carrier. In certain configurations, a UE may find a carrier that has a desired LAA cell (e.g., belonging to desired PLMN) and measure a high RSRP for the cell. On a different carrier the UE may find a desired LAA cell and measure a moderate RSRP for the cell. Based on the current measurement framework, the first cell would be chosen for LAA service. However, if the first carrier has a significantly higher level of activity/channel occupancy compared to the second carrier, the throughput that can be achieved on the first cell may be lower than the throughput that can be achieved on the second cell. Moreover, for certain types of services (e.g., VoIP and other periodic packet arrival services) a carrier with low occupancy may be preferred.